1. Field of the Invention
The present invention relates to an apparatus for separating suspended solids from a suspension. More particularly, it relates to a solid-liquid separator with a filtering section and a sedimenting section combined together, in which a particulate filter material is floated in a suspension and which is designed so as to effectively backwash such a floating filter bed.
2. Description of the Prior Art
The clarification and filtration of suspended solids from a suspension has heretofore been carried out generally by means of a plurality of apparatuses as will be described in detail hereinbelow. This arrangement comprises mainly a separate combination of a clarifier and a filter. In a system having the arrangement described hereinabove, the filter is usually of a fixed-bed type in which a prefilt liquid is designed so as to flow downward and pass through the filter bed. The filter is generally a two-layer construction in which an upper layer that is made usually of sand having a filtering ability and finer particle size is arranged on top of a lower layer of coarser sand having substantially the same thickness. This construction, however, requires a large apparatus. This type of the apparatus arrangement has various additional disadvantages: i.e. its large space requirements, its operation complexity, its long-term backwashing time requirements, its necessity of a large amount of backwash liquor, its high cost, its required large number of laborers per unit time for building equipment and for carrying out operations, and its complex arrangement for transporting liquids.
Accordingly, some attempts have heretofore been made to improve the disadvantages of the conventional arrangements. A first attempt is said to be to combine a clarifier and a filter into one apparatus. Such an apparatus has been proposed as shown in U.S. Pat. No. 3,558,482 to Young. This apparatus employs a granular filter bed of graphite ore or anthracite ore or the like. It is stated that such beds may operate for long periods of time without backwashing. Since the apparatus adopts a fixed bed system, however, the disadvantages inherent in conventional filters using fixed beds are not said to be improved to a great extent. The system in the improved apparatus similarly requires complicated operating procedures and a large amount of water for backwashing. Moreover, any effective backwashing may not be expected so long as the fixed bed system is adopted.
Other attempts at improving the disadvantages involved in conventional apparatus arrangements have also been proposed in which a particular filter material is employed. One example of such an arrangement is an apparatus as shown in Japanese Patent Publication No. 5947/1960, in which the apparatus is arranged such that a filter is placed on top of a clarifier and two sections are partitioned by a perforated support plate. A granular filter material is held in the filter section. This type of apparatus generally comprises a floating filter bed and a means for discharging a rinsing liquid against the filter bed, such as a shower or a spray head with a plurality of nozzles along the header. The operation of such an apparatus will be described in detail hereinbelow. The apparatus may obviate some disadvantages of the conventional type apparatus arrangement in a separate construction with respect to the complex operation and large-scale equipment requirements, but the other disadvantages of the conventional separate-type apparatus arrangement have not been improved. An additional disadvantage of the apparatus of this type is that the cleaning of the filter bed by spraying a rinsing liquid against the bed in such a manner cannot give a satisfactory rinsing effect, thereby reducing the period of filtration to a great extent. This is true even where air is used for cleaning the filter bed in the apparatus instead of water.